* gnu/packages/patches/icecat-use-system-harfbuzz.patch,
gnu/packages/patches/icecat-use-system-graphite2.patch: New files.
* gnu/local.mk (dist_patch_DATA): Add them.
* gnu/packages/gnuzilla.scm (icecat)[source]: Add patches. Delete
"gfx/harfbuzz" and "gfx/graphite2" in the snippet.
[inputs]: Add harfbuzz and graphite2.
[arguments]: Add "--with-system-harfbuzz" and "--with-system-graphite2" to
configure-flags.